Such a component and a method for producing same are known from DE 37 33 693 A1.
The known component is a temperature-dependent switch, which, in a known manner, depending on its temperature, produces an electrically conductive connection between the two connection surfaces.
Such temperature-dependent switches are used for being connected in series in the power supply circuit of an electrical appliance to be protected and at the same time for being coupled thermally to the electrical appliance to be protected.
As long as the electrical appliance to be protected is at a temperature which is below a response temperature of the temperature-dependent switch, said switch therefore remains closed and the current flows through the electrical appliance. If the temperature of the electrical appliance now increases to an impermissible value, the switch is opened and the circuit is interrupted.
An example of such a temperature-dependent switch is described, for example, in DE 21 21 802 A1 and DE 196 03 310 A1, the contents of said documents hereby incorporated by reference into the subject matter of the present application.
In the case of the switch known from DE 21 21 802 A1 and DE 196 03 310 A1, a temperature-dependent switching mechanism with a snap-action bimetallic disc and a snap-action spring disc which is supported with its edge on the housing lower part and bears, in the centre, a movable contact part which interacts with a fixed contact part on the cover part of the switch is provided. In this way, an electrically conductive connection between the cover part and the lower part is provided, with in each case one connection surface for the connection of connecting strand wires being provided on the cover part and the lower part.
The snap-action bimetallic disc is enclosed loosely in the switching mechanism below its response temperature and is not involved in the current conduction. If the temperature now increases above the response temperature of the snap-action bimetallic disc, said snap-action bimetallic disc changes its configuration and in the process presses the movable contact part away from the stationary contact part, counter to the force of the snap-action spring disc, with the result that the switch is opened.
If the temperature of the switch is decreased again, with the result that it ultimately decreases to a value below the spring-back temperature of the snap-action bimetallic disc, said bimetallic snap-action bimetallic disc springs back into its original configuration and closes the switch again.
If this automatic closure is undesirable, the known switch can be provided with a so-called self-holding resistor, which is arranged electrically in parallel with the connection surfaces. If the temperature-dependent switch now opens at an excessively high temperature of the electrical appliance to be protected, a residual current flows through this self-holding resistor, which is preferably manufactured from a material with positive temperature coefficients.
In this PTC thermistor, so much ohmic heat is then developed by the residual current that the snap-action bimetallic disc is held at a temperature above its spring-back temperature until the circuit is opened actively.
A temperature-dependent switch with a self-holding function is used in particular when frequent reconnection of the electrical appliance to be protected is undesired or results in damage, such as, for example, in the case of a mechanically jammed wash water pump, whose impeller first needs to be cleaned before the pump can start up again.
Such a self-holding temperature-dependent switch is known from DE 37 10 672 A1.
If the current to be guided through the temperature-dependent switch is in the range of several amperes, the current is conducted preferably no longer via the snap-action spring disc, but via a current transfer element, which is moved by the snap-action spring disc and interacts with two stationary contacts, which are arranged on the cover of the temperature-dependent switch. The operating current of the electrical appliance to be protected flows through this current transfer element.
Such a temperature-dependent switch is known from DE 26 44 411 A1 or DE 197 08 436 A1.
This temperature-dependent switch can also be provided with a self-holding function, as is known, for example, from DE 197 27 197 A1 .
Finally, it is also possible to provide said four types of switch, as described above, with a so-called current dependency, with the result that the switches open not only in the event of an excessively high operating temperature of the electrical appliance to be protected, but also at an excessively high operating current. For this purpose, a series resistor is connected in series with the external terminals of the switch, said series resistor heating up in the event of an excessively high current flow to such an extent that the snap-action bimetallic disc is heated to a temperature above its response temperature.
Such current-dependent and temperature-dependent switches are known, for example, from DE 44 28 226 A1 and DE 197 48 589 A1.
All of the above described temperature-dependent switch types can be provided, in accordance with the invention, with a protective housing, as is known from DE 37 33 693 A1 mentioned at the outset.
Although the known temperature-dependent switches already have a housing which protects against the ingress of dust and moisture, in many cases it is still desirable to protect the switch and the electrical connections of the connecting cables to the connection surfaces from aggressive media or else merely from dust and moisture.
That is to say that the known switches are often used in environments in which high mechanical loads, high pressures, high moisture levels or else solvent vapours or vapours from transformer oil etc. occur.
In particular the ingress of moisture, solvent vapours or other gases into the interior of the switch is also disadvantageous because the snap-action bimetallic discs and snap-action spring discs can be attacked thereby and the quality of the contact surfaces on the stationary and movable contact parts can be impaired.
Against this background, DE 37 33 693 A1 proposes introducing the temperature-dependent switch into a metal housing which is then welded shut and using a compression-glass bushing as cable bushing, through which the connecting cables are passed out of the interior of the metal housing.
DE 101 10 562 C1 has disclosed providing particular adhesive-bonding measures in order to seal the interface between the housing lower part and the housing upper part of a temperature-dependent switch.
DE 197 54 158 A1 has disclosed introducing a temperature-dependent switch with a housing and soldered-on connecting lines into a hose-shaped sleeve and then sealing this sleeve at its open end, from which the connecting lines protrude, with the aid of a closure means and under the effect of heat.
However, until now all of these measures have not been able to ensure that gases and liquids nevertheless do not enter the interior of the protective housing, and from there also the housing of the temperature-dependent switch, under loading environmental influences.
These gases and moisture diffuse or creep into the interior of the protective housing at the interfaces between the connecting cables and the cable bushings and between the cable bushings and the protective housings.